British Prime Minister Theresa May announced the expulsion of 23 Russian diplomats from the U.K. Wednesday, a retaliatory move for the nerve agent attack on a former spy and his daughter in the city of Salisbury. On Monday, May said it was “highly likely” that Russia was behind the attack. She went a step further Wednesday in a speech to Parliament.

“This represents an unlawful use of force by the Russian state against the United Kingdom,” May said. “It must therefore be met with a full and robust response.”

May reiterated the British conclusion that Russia was behind the attack, which targeted 66-year-old former Russian spy Sergei Skripal and his 33-year-old daughter Yulia. Both remain hospitalized, as does a police officer who first tried to assist them on a park bench in Salisbury. Hundreds more have been warned about possible exposure to the nerve agent.

Along with expelling the diplomats, May said the U.K. has suspended high level diplomatic talks with Russia, called off a planned visit by Russian Foreign Minister Sergei Lavrov and vowed to keep British ministers and royals away from this summer’s World Cup in Russia.

“For those who seek to do us harm, my message is simple. You are not welcome here,” May said.

Russia remains defiant in the face of the accusations. Lavrov on Wednesday blamed Britain for “acting out political drama” and suggested that the attack wasn’t carried out by Russia at all. Instead, he suggested that the country was framed by “those who want to continue a campaign of Russophobia.”